With the amazing progress of the Internet, data services are being rapidly set up in a mobile network which has mainly offered voice-based services. As a consequence, it is likely that data traffic will surpass voice traffic sooner or later. Against such a background, 3GPP (3rd Generation Partnership Project) and 3GPP2 are working on an ALL IP network to develop a voice-based network into a suitable network for the mobile Internet. Besides, in IETF (Internet Engineering Task Force), the Mobile IP WG (working group) to originally discuss IP mobility in the use of LAN comes to consider standardization of a third-generation mobile communication system. Especially, as IPv6 is to replace IPv4 in which there is concern about address deficiencies in the future, IP mobility in IPv6 (Mobility Support in IPv6 <draft-ietf-mobileip-ipv6-12. txt>) is an intensely studied topic in the WG.
According to IPv4 and IPv6, a node that continually moves and changes the connected subnetwork is called “mobile node”, the subnetwork to which the mobile node was originally connected is called “home network”, a node that is present in the home network and takes charge during the absence of the mobile node is called “home agent”, a subnetwork to which the mobile node is actually connected is called “foreign network”, a node that is present in the foreign network to look after the mobile node while it is in the foreign network is called “foreign agent”, an address that is assigned for the mobile node in the foreign network is called “c/o address” (Care-Of Address; abbreviated to CoA), and an address that is uniquely assigned for the mobile node independently of the connected subnetwork is called “home address”. Incidentally, since the mobile node itself and IPv6 mechanism assume the role of the foreign agent, the foreign agent does not exist in IPv6. In addition, the correspondent nodes (Correspondence) of the mobile node include fixed nodes as well as other mobile nodes.
Set out below are general processes according to IPv4 and IPv6.
(1) In the Case where the Mobile Node is in the Home Network
As with the case of ordinary TCP/IP, the mobile node communicates with a correspondent node in the ordinary way.
(2) In the Case where the Mobile Node is not in the Home Network
When the mobile node detects that it is in a network other than the home network, it makes a “binding update request” to notify the home agent of a new CoA through the foreign agent so that all packets to its home address are forwarded to the mobile node. In the case of IPv6, the mobile node sends the binding update request directly to the home agent as shown in FIG. 8.
(2-1) The Arrival of Packets
The packets sent from the correspondent node to the home address arrive at the home network through the mechanism of normal IP routing. The home agent catches the packets by Proxy ARP or the like, and carries out encapsulation to tunnel them to the foreign agent in the network where the mobile node is present. Thus, the mobile node receives the packets via the foreign agent. In IPv6, the mobile node that has received tunnelled packets transmits a new registration request to the correspondent node that sent the packets and notifies the correspondent node of a CoA, as shown in FIG. 8. After that, the correspondent node transmits packets directly to the mobile node using the CoA.
(2-2) The Transmission of Packets
When the mobile node transmits packets to the correspondent node, the header of each IP packet still contains the home address as a source address. In the case where any error occurs on the way, the packets are sent to the home address and, consequently, returns to the mobile node through the above-mentioned mechanism. In the case of IPv6, a CoA is set as the source address, and the home address is indicated as a newly defined destination option.
Additionally, in conventional Mobile IPv6, when a MN (Mobile Node) moves from one subnetwork to another, the MN sends a registration request (Binding Update: hereinafter also referred to as BU) to its HA (Home Agent). In the case where packets from a correspondence node (CN) have been forwarded to the MN through the HA by tunneling as in Mobile IPv4, the MN sends binding update information including a pair of its home address and CoA to the CN on the assumption that the CN has no knowledge of the CoA of the MN. After that, the CN can transmit packets directly to the MN. Herewith, in Mobile IPv6, it is possible to support the route optimization feature for resolving the problem of triangle routing which is a drawback of Mobile IPv4.
Moreover, Mobile IPv6 supports the smooth handoff feature for avoiding a packet loss on the occasion of a handoff. While Mobile IPv6 has improvements over Mobile IPv4, it adopts a flat HA-MN network model as with Mobile IPv4. On this account, the problem of round trip delay is yet not overcome. That is, in the case, for example, where the MN “roams” to a network which is physically distant from the HA, the registration request is delayed by round trip time between the MN and HA. In order to solve the problem, there has been proposed an Internet-Draft (hereinafter referred to as I-D) “Hierarchical Mobile IPv6 mobility management” <draft-ietf-mobileip-hmipv6-01.txt>. According to the I-D, a hierarchical network model comprised of MN-AR (Access Router)-MAP (Mobility Anchor Point)-HA is introduced in Mobile IPv6 as shown in FIG. 17. In the Hierarchical Mobile IPv6, the MAP supports the agent function of the HA to thereby reduce the aforementioned delay in the registration request from the MN.
Besides, according to another I-D “Homeless Mobile IPv6” <draft-nikander-mobileip-homelessv6-00.txt> proposed in the IETF WG held from December 11 until Dec. 15, 2000, the HA and home address are not required as shown in FIG. 18. Originally, in Mobile IPv6, the Binding Updates exchanged between the MN and CNs are used for sharing movement/mobility management information between the MN and CNs. In the Homeless Mobile IPv6, the Binding Update is continued, and the MN retains information called “Host Cache”. Thus, it is made possible to implement the movement/mobility management without the HA. As the merit of the Homeless Mobile IPv6, it is indicated in the I-D that the communication between two Homeless supporting Hosts does not require the routing header and home address destination option which are used in Mobile IPv6, and a packet can be transmitted/received by the use of the IPv6 header only. Thus, the header size for the packet can be reduced from 92 to 40 bytes.
Problems that the Invention is to Solve
In the case of IPv4, there is the problem of so-called triangle routing since packets addressed to the mobile node are inevitably transmitted via its home agent. In addition, packets sent from a correspondent node to the mobile node are intercepted by the home agent, and encapsulated and tunnelled to the foreign agent in the network where the mobile node is present. After that, the foreign agent carries out de-capsulation to forward the packets to the mobile node. Such packet encapsulation in the home agent may cause bottlenecks in scaling the packets to fit in a large-scale mobile network.
In the case of IPv6, the mobile node which has received tunnelled packets notifies the correspondent node of the CoA as a binding update request on the assumption that the correspondent node has no knowledge of the CoA, and the correspondent node transmits packets directly to the mobile node using the CoA. This helps to solve the triangle routing problem, a drawback of Mobile IPv4. However, the first packet sent from the correspondent node that has not yet learnt the CoA of the mobile node is inevitably forwarded via the home agent. Therefore, the triangle routing problem remains unresolved with regard to the first packet.
Moreover, according to IPv6, a function for sending binding update requests to correspondent nodes is not an essential function of the mobile node. The mobile node “MAY”, in IETF parlance, sends binding update requests, which means that not all the mobile nodes support the binding update function. For this reason, in an advanced mobile network with IPv6, there is apprehension that the problems of triangle routing and packet encapsulation in the home agent may remain unchanged from IPv4.
On the other hand, in the case where the mobile node and correspondent nodes (mobile node, etc.) exchange binding update requests with each other to update information on association between the home address and CoA of each node so that packets can be sent directly to the CoA from the first one, the mobile node has to send/receive binding update requests with considerable frequency if it has many correspondent nodes. Since the mobile node on standby is required to enter transmission mode for transmitting the binding update requests, its battery drain is hastened. In addition, when binding update requests are exchanged between mobile nodes, the binding update requests create a large amount of traffic in radio sections in a large-scale mobile network. The traffic leads to consumption of radio resources to be reckoned with.
The Hierarchical Mobile IPv6 mobility management has shortcomings as described below. The following is an excerpt from 6.1 Mobile node Operation in the I-D:                “The MN may also send a similar BU (i.e. that specifies the binding between the Home Address and the RCoA) to its current correspondent nodes.”        
That is, as in Mobile IPv6, the MN has to exchange Binding Updates with CNs (MN, etc.) so that each of them can update binding update information. Since the binding update information needs to be updated every time the mobile node moves from one area to another and also refreshed at regular intervals, the mobile node has to send/receive Binding Updates with considerable frequency when it has many CNs to exchange Binding Updates with. The MN on standby is required to enter transmission mode for transmitting Binding Updates, and therefore its battery drain is hastened. Additionally, the MN needs resources (memory, CPU load) to store the binding update information, which affects the miniaturization of the MN as well as the life of its battery.
The following is another excerpt from 6.1 Mobile node Operation in the I-D:                “The MAP will receive packets addressed to the mobile node's RCoA (from the HA or correspondent nodes). Packets will be tunnelled from the MAP to the mobile node's LCoA. The mobile node will de-capsulate the packets and process them in the normal manner.”        
As is described previously, in Mobile IPv4, packets sent from a CN to the MN are intercepted by the HA, and encapsulated and tunnelled to the FA (foreign agent) in a network visited by the MN. Having received the packets, the FA de-capsulates the packets and forwards them to the MN. Such packet encapsulation in the home agent may cause bottlenecks in scaling packets to fit in a large-scale mobile network. Similarly, in the Hierarchical Mobile IPv6, the MAP encapsulates packets sent from a CN to the MN. Accordingly, the amount of encapsulation process is considered to become a concern in a large-scale mobile network.
Besides, the Homeless Mobile IPv6 has shortcomings as described below. The Homeless Mobile IPv6 also has problems of battery drain of the MN and consumption of radio resources by binding update traffic in a large-scale mobile network because the MN and CNs update their Host Caches using Binding Updates as in the Hierarchical Mobile IPv6. Moreover, in the communication between two Homeless supporting Hosts, it is conceivable that both of them enter new domains at the same time and lose radio links. In this case, both the hosts lose each other's location information (new address information) at once if the worst happens. With this architecture, each of the hosts does not have any means for notifying its correspondent host of a change in address. Incidentally, it may be presumed that this problem does not arise when the correspondent host is a fixed node. Further, when a mobile host receives packets from an unknown or new host for the first time, the new host does not have any means for learning the address of the mobile host. In both cases, support for the HA function is required.
Problems described above are summarized as follows:
(1) the problem of battery drain of the mobile node due to exchanges of binding update requests between the mobile node and correspondent nodes;
(2) the problem of consumption of radio resources due to exchanges of binding update requests between the mobile node and correspondent nodes; and
(3) the problem of scalability to a large-scale mobile network encountered in the process of encapsulating packets to the mobile node in the home agent.
It is therefore an object of the present invention to provide a mobile node managing system which solves the aforementioned three problems associated with the prior art.